Nitrided titanium surfaces with a natural titanium color

Abstract

This application relates to an enclosure for a portable electronic device. The enclosure includes a titanium substrate having interstitial nitrogen atoms, where the titanium substrate is characterized as having an a* value that is less than 1, a b* value that is less than 5, and an L* value that is more than 70.

What is claimed is: 
     
       1. An enclosure for a portable electronic device, the enclosure comprising:
 a titanium substrate defining an external surface, the titanium substrate comprising at least 10 at % interstitial nitrogen atoms at or near the external surface, the titanium substrate having an a* value that is less than 1 and a b* value that is less than 5. 
 
     
     
       2. The enclosure of  claim 1 , wherein the titanium substrate has a surface hardness of 850 HV 0.1  or greater. 
     
     
       3. The enclosure of  claim 1 , wherein the titanium substrate has an L* value of 65 or more. 
     
     
       4. The enclosure of  claim 1 , wherein the color is characterized according to CIE L*a*b* color-opponent dimension values. 
     
     
       5. The enclosure of  claim 1 , wherein the titanium substrate has a surface hardness of 850 HV 0.1  or greater and a hardness of the titanium substrate decreases as a depth from the external surface increases. 
     
     
       6. The enclosure of  claim 1 , wherein the titanium substrate includes a chemically etched external surface. 
     
     
       7. The enclosure of  claim 1 , wherein the titanium substrate has a thickness of at least 10 μm or greater. 
     
     
       8. The enclosure of  claim 7 , further comprising:
 a metal oxide layer that overlays the titanium substrate. 
 
     
     
       9. The enclosure of  claim 8 , wherein the metal oxide layer is modified to exhibit a range of colors relative to a thin film interference effect. 
     
     
       10. An enclosure for a portable electronic device, the enclosure comprising:
 a titanium substrate; and 
 a titanium nitride layer overlaying the titanium substrate, the titanium nitride layer comprising at least 10 at % interstitial nitrogen atoms and having a thickness of less than 100 μm, the titanium nitride layer having an a* value less than 1 and a b* value less than 5. 
 
     
     
       11. The enclosure of  claim 10 , wherein the interstitial nitrogen atoms are uniformly dispersed throughout the titanium nitride layer. 
     
     
       12. The enclosure of  claim 10 , wherein the color is characterized according to CIE L*a*b* color-opponent dimension values. 
     
     
       13. The enclosure of  claim 10 , further comprising:
 an anodized layer that overlays the titanium nitride layer. 
 
     
     
       14. The enclosure of  claim 10 , wherein the titanium nitride layer has an external surface that is blasted, textured or polished.